In Label Switching networks, such as Multi-Protocol Label Switching (MPLS) networks Label Switched Paths (LSPs) are established to route traffic along specified paths through the network. An LSP is established by means of signaling using path messages that are distributed to the Label Switched Routers (LSRs) along the LSP.
It is possible to set up point-to-point LSPs between one ingress LSR and one egress LSR as well as point-to-multipoint (P2MP) LSPs between one ingress LSR and a plurality of egress LSRs. P2MP LSPs may e.g. be used for multicasting in the case of an IP-TV application. A P2MP LSP is comprised of multiple source-to-leaf (S2L) sub-LSPs. These S2L sub-LSPs are set up between the ingress and egress LSRs and are appropriately combined by means of propagating path messages that encodes the P2MP LSP to all the branches of connected LSRs that form the P2MP LSP.
There are known mechanisms and semantics that have been developed for setting up LSPs. The IETF RFC 3209 “RSVP-TE: Extensions to RSVP for LSP Tunnel”, December 2001 defines a mechanism for setting up P2P Traffic Engineered LSPs in Multi-Protocol Label Switching (MPLS) networks. The IETF RFC 3473 “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions”, January 2003, defines extensions to the above mentioned RFC 3209 for setting up P2P TE LSPs in Generalized MPLS (GMPLS) networks. However these specifications do not provide a mechanism for building point-to-multipoint (P2MP) TE LSPs.
The IETF RFC 4875 “Extensions to Resource Reservation Protocol-Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)”, May 2007, defines extensions to the RSVP-TE protocol described in the above RFC 3209 and RFC 3473 to support P2MP TE LSPs satisfying the set of requirements described in the IETF RFC4461 “Signaling Requirements for Point-to-Multipoint Traffic-Engineered MPLS Label Switched Paths (LSPs)”, April 2006. The RFC 4875 relies on the semantics of the Resource Reservation Protocol (RSVP) that RSVP-TE inherits for building P2MP LSPs.
The RFC 4875 describes a compression mechanism for encoding a P2MP LSP that is based on explicit encoding of one S2L sub-LSP. For other S2L sub-LSPs of the P2MP LSP only the path from a branch LSR to the egress LSR of that S2L sub-LSP is explicitly encoded. Thus by means of this compression mechanism extra processing that can result if explicit routes are encoded from ingress to egress for each S2L sub-LSP is reduced and the sizes of Path messages is also reduced.
However, setting up P2MP LSPs with complex topologies still requires a very large number of bytes of signalling information. There is therefore a need for methods and arrangements that are able to set up P2MP LSPs more efficiently than the methods and arrangements according to prior art.